The present invention relates to a motor vehicle with an anti-blocking brake system in which the brake force at the wheel brakes of the rear wheels are regulated at some time on the basis of the wheel movement behavior of the wheel tending to block first and at some time on the basis of the wheel movement behavior of the wheel tending to block last, referred to as "select low" and "select high" regulatory method.
Motor vehicles which are equipped with an anti-blocking brake system (ABS), respectively, with an automatically blockable differential (ASD) are generally known.
For the regulation of the brake force at the wheels of the rear axle, the so-called "select low" method is generally used in an ABS; this means a common regulation of both wheels in dependence on the rotational behavior of the wheel with the lower traction coefficient.
This method was introduced in order to keep as small as possible and controllable the yaw reaction of the vehicle (rotation about the vertical axis) if different traction coefficients occur at the wheels (so-called "asymmetric road surface").
This reduction of the yaw reaction is accepted with a lengthening of the brake path because with differing traction coefficients too little brake pressure is always supplied to the wheel with the higher traction coefficient.
The present invention is therefore concerned with the task to provide an arrangement with the aid of which it is possible at least in the case of a regulated braking on an asymmetric road surface to reduce the possible brake path up to standstill of the vehicle.
The underling problems are solved according to the present invention by an electronic unit which, in dependence on a comparison of at least one value pair of instantaneous vehicle velocity and instantaneous vehicle cross-acceleration with predetermined threshold values, produces an output signal which, in case of a four-channel ABS, effects a shifting of the regulating method of the ABS from "select low" to "select high", in case of a three-channel ABS, effects a shifting of the predetermined slippage threshold value to a higher value and with a vehicle equipped with an ABS and an ASD effects in case of a regulated braking a switching-on of the ASD.
In order not to provoke a sudden yaw reaction of the vehicle as a result of this shifting, respectively, switching-on, provision is made according to the present invention to permit at least at higher vehicle velocities the rise of the brake pressure at the wheel with the higher traction coefficient, respectively, the increase of the slippage threshold, respectively, the rise of the locking action of the ASD only with a predetermined preselectable velocity increase.
It is possible in this manner to reduce the braking path without causing any significant yaw reactions.
As the shifting from "select low" also goes in the direction of a reduction of the lateral guide force, provision is made according to the present invention to predetermine minimum track radii, respectively, maximum cross-accelerations in dependence on the vehicle velocity which must not be dropped below, respectively, exceeded.